This invention relates to an infrared thermometer for measuring the temperature of a target by sensing infrared radiation emitted from the target.
One application of an infrared thermometer is to use it as an infrared clinical thermometer for measuring the temperature (body temperature) of the human body. This thermometer generally performs temperature measurement based upon infrared radiation emitted from the external ear canal or tympanic membrane, etc., of the human ear.
An infrared clinical thermometer is equipped with a probe insertable into the ear orifice, and the probe is provided within the clinical thermometer body (housing) so as to protrude to the outside. Provided within the probe is a waveguide for guiding infrared radiation, which is emitted from the tympanic membrane or the like (biological surface tissue), to an infrared sensor disposed inside the housing.
One important problem with an infrared clinical thermometer is that when the probe is inserted into the ear orifice, heat is transferred from the ear orifice (human body) to the infrared sensor via the probe and waveguide, as a result of which the output of the infrared sensor becomes unstable. The adverse influence of heat from the surrounding environment transferred from the housing to the infrared sensor also cannot be ignored.
One technique which solves this problem is as described in the specification of Japanese Patent Publication No. 5-28617 (or U.S. Pat. No. 4,895,164 or WO 90/02521). According to the infrared clinical thermometer disclosed in these references, the larger portion of the waveguide and the infrared sensor are embedded in a comparatively large heat conducting block (isothermic block means) made of metal (an excellent thermal conductor such as aluminum or copper). The heat conducting block (the infrared sensor portion) is supported inside the housing by a spacer stand, and a space between the heat conducting block and housing acts as an insulative air layer to reduce the migration of heat from the heat source outside the housing to the heat conducting block. It is stated that the waveguide and infrared sensor are held in an isothermic state at ambient temperature by the heat conducting block. Furthermore, a low-emissivity barrier such as an aluminum tube is placed around the outer end of the waveguide, and the barrier is covered by a cover of low thermal conductivity.
One feature of an infrared clinical thermometer is short measurement time (e.g., 1 to 5 seconds). Since the heat conducting block in the foregoing references is comparatively large, a state of thermal equilibrium (temperature equalization) is not attained in such a short period of time. As long as heat from the human body travels to the heat conducting block by being transmitted along the waveguide, the temperature of the infrared sensor also will vary. Thus the instability of the output from the infrared sensor is a problem that has not been solved satisfactorily.
A technique intended to solve this problem is illustrated in the specification of International Patent Laid-Open No. WO 97/24588. According to the infrared thermometer described in this reference, a heat conductive tubular body is provided between a probe and a waveguide in a state thermally insulated therefrom, and heat from the probe is prevented from being transmitted to the waveguide and infrared sensor. The provision of the heat conductive tubular body increases the number of component parts.
Another problem with infrared thermometers is that dust or the like penetrates the interior of the waveguide, resulting in reduced measurement precision.
In order to solve this problem, the conventional practice is to bond silicon glass to the opening at the tip of the waveguide to close the same. However, problems encountered with silicon glass are difficulty in working the glass and the high price thereof. In addition, fabrication cost rises owing to the use of a bonding agent.
A method available is to close the opening at the tip of the waveguide by covering it with a resin film and secure the resin film to the waveguide by a ring member. The problems with this method are the labor required for assembly and the fact that the resin film tears easily when contaminants are wiped off.
An infrared clinical thermometer has a temperature range (measurable temperature range) (e.g., 10xcx9c40xc2x00 C.) within which it is capable of operating normally. An error is displayed if an attempt is made to use an infrared clinical thermometer in an environment where the temperature is outside this temperature range. A further problem is inconvenience in that the user cannot determine why an error display is being presented nor how long it will take before the thermometer can be used.
An object of the present invention is to make it possible to measure temperature accurately, with simple structure, by reducing, to the maximum degree, the influence exerted upon an infrared sensor by heat transferred from the outside (a target such as the ear canal) to a waveguide.
Another object of the present invention to provide a structure that is capable of alleviating the adverse effects of environmental temperature.
A further object of the present invention is to effectively prevent dust or the like from penetrating the interior of a waveguide in an infrared thermometer and to implement this in such a manner that assembly is facilitated.
Still another object of the present invention is to so arrange it that the length of time needed before measurement becomes possible is shown clearly when an infrared thermometer in a temperature environment in which measurement is impossible is placed in a temperature environment in which measurement is possible.
The present invention provides an infrared thermometer having an infrared sensor placed inside a housing and a waveguide for guiding infrared radiation, which is emitted from a target, to the infrared sensor, characterized in that the infrared sensor and waveguide are held in direct or indirect contact with the housing in a state in which the infrared sensor is thermally insulated from the waveguide.
There are various modes available for supporting the infrared sensor in a state in which it is thermally insulated from the waveguide. The waveguide has an outer end that opposes the target and an inner end that opposes the infrared incidence surface (sensor surface) of the infrared sensor. In one of the above-mentioned modes, the inner end of the waveguide is spaced apart (by provision of a gap) from the infrared incidence surface of the infrared sensor. An air layer is present between the inner end of the waveguide and the infrared sensor, and the air layer has a heat insulative effect.
The waveguide and infrared sensor can be held in the housing by a common heat insulating member or by separate heat insulating members. Synthetic resin is a typical example of the heat insulating member (a member of low thermal conductivity). It may be so arranged that the waveguide is supported by a metal member (a member having excellent thermal conductivity).
In another mode of supporting the infrared sensor in a state in which it is thermally insulated from the waveguide, the infrared sensor is placed inside the inner end of the waveguide and the infrared sensor is held spaced away from an inner wall of the waveguide. In this case also an insulative air layer is provided between the waveguide and infrared sensor.
The infrared sensor and the waveguide can be held in the housing by a common heat insulating member or by separate heat insulating members. The infrared sensor may be supported by providing a heat insulator between the infrared sensor and waveguide.
In yet another mode, the infrared sensor can be supported on the inner end of the waveguide by a heat insulating (low thermal conductivity) connecting member. The infrared incidence surface of the infrared sensor opposes the inner end of the waveguide. The waveguide is supported on the housing by a heat insulating member or metal.
Further, such a mode is covered by the present invention in which the infrared sensor is held in a state in which it is thermally insulated from the waveguide that the inner end of the waveguide is in contact with the infrared incidence surface of the infrared sensor. Preferably, the inner end of the waveguide is formed to have notches to reduce the area of surface contact with the infrared sensor.
Thus, in accordance with the present invention, the infrared sensor is held in a state in which it is thermally insulated from the waveguide (a state in which there is low thermal transfer). Even if heat is transferred from the target to the waveguide, therefore, the transfer of heat from the waveguide to the infrared sensor is suppressed. As a result, the infrared sensor is held in a thermally stable state.
The present invention is characterized in that the infrared sensor is thermally insulated (spaced away) from the waveguide; the infrared sensor and waveguide are not rendered isothermic. In other words, the present invention is devoid of means corresponding to the heat conducting block or isothermic block means of the kind in the prior art. Furthermore, there is no heat conductive tubular body provided between the probe and the waveguide in a state thermally insulated therefrom. The result is a simple structure for the infrared thermometer.
Holding the infrared sensor by the heat insulating member makes it possible to minimize the effects of heat transferred from the outside via the housing and other members.
In a preferred embodiment, a probe, which is formed by a heat insulating member surrounding a part of the waveguide protruding externally of the housing, is attached to the housing, and a gap is provided at least between the outer end of the waveguide and the probe. Even if the probe contacts the target, the transfer of heat from the target to the waveguide is suppressed because the waveguide is spaced away from the probe within the probe (because of the presence of an insulative air layer).
The present invention further provides a cap which covers the waveguide of the infrared thermometer.
The cap has an infrared-transparent upper bottom for closing an opening in the outer end of a waveguide, and a circumferential wall portion contiguous to the upper bottom and in intimate contact with the periphery of the waveguide, the upper bottom and circumferential wall portion being formed as an integral body. In a preferred embodiment, the cap is made of synthetic resin.
Because the cap (the waveguide cap) according to the present invention is obtained by integrally forming the infrared-transparent upper bottom and circumferential wall portion, the waveguide need merely be covered by the cap, thereby providing ease of operability and ease of assembly superior to prior art. The cap prevents dust from penetrating the interior of the waveguide.
In an embodiment, the waveguide cap has an outwardly or inwardly directed flange provided on the circumferential wall portion. The flange acts to retain the waveguide cap. The waveguide preferably is provided with a portion for engaging with the flange. This enhances the retention effect greatly.
The present invention further provides an infrared thermometer capable of clearly indicating length of time until measurement is possible when the infrared thermometer located in a temperature environment in which measurement is impossible is placed in a temperature environment in which measurement is possible.
The infrared thermometer includes: infrared measurement means for measuring temperature of a target based upon an output of an infrared sensor; temperature measurement means for measuring temperature within the infrared thermometer; means for determining whether the temperature measured by the temperature measurement means lies within a measurable temperature range of the infrared measurement means; means for estimating waiting time that would be needed for the temperature measured by the temperature measurement means to fall within the measurable temperature range when the determination means has determined that the measured temperature does not lie within the measurable temperature range; and means for giving notification of the waiting time that has been estimated by the estimation means.
In a preferred embodiment, the estimation means senses a change in temperature at least at two different times and estimates the waiting time based upon this temperature change, current temperature and target (reference) temperature within the measurable temperature range.
Since the waiting time is reported (displayed), the user can ascertain how much time must pass before the infrared thermometer can be used.